It is the conventional practice to sterilize in advance the interior of bottles and other vessels upon filling them with contents. Patent Document 1 (JP2001-39414A) discloses sterilizing the interior of a blow-molded bottle by introducing mist of a sterilizing agent into the bottle. Patent Document 2 (JP2000-326935A) discloses sterilizing the interior of a preform by dripping the preform into a germicidal solution before blow molding.